Mountain Pine Beetles on Rockies Eastern Slope Offer Improved Perspectives
Editor’s Note: If you live in the Canadian Rockies, there’s no doubt you’ve seen the large swathes of red (dead) trees from pine beetle kill. Depending on how you look at them, they can be aesthetically pleasant or a cause for concern.
In this piece from Felix Sperling, he educates us on pine beetles and the effects of their kill. Will logging the trees help? Are they really the fire hazard we think they are? Are all pine beetles the same? Read on to learn more…
This article first appeared in the 2019 State of the Mountains Report. We'll continue to publish articles exploring the science on our current state of Canada's alpine on our blog throughout the year. Find them all here.
View south from Old Fort summit, Jasper. Photo: Z. MacDonald.
Expanding beetle kill
Mountain pine beetles (Dendroctonus ponderosae) are now threatening pine forests along the full length of the eastern slopes of the Canadian Rockies. But that doesn’t mean it is clear what we should do about them. Their populations expanded across the western states and British Columbia in the 1990s and 2000s, driven by a combination of global climate change, forest management and fire suppression practices. The beetles overwhelmed lodgepole pine and other pines across BC, peaking in 2005 and killing more than half of all merchantable pine in BC by 2012.¹ In Alberta, beetle flights in the north went far past Grand Prairie in 2006, while in the south they reached Canmore and Banff. More recently, beetles have swept across Jasper National Park toward Hinton, creating a new front. Small infestations have now also been detected in the previously untouched area between Hinton and Canmore, including near Rocky Mountain House.² Like in BC, the extensive, mature lodgepole pine forests of west-central Alberta may not survive long, and mountain pine beetles could then sweep across the boreal jack pine forest into eastern Canada.¹
“This slow-building crisis has brought out several conflicting visions of what the forests of the eastern slopes of the Rocky Mountains should do for us.”
This slow-building crisis has brought out several conflicting visions of what the forests of the eastern slopes of the Rocky Mountains should do for us. The region provides tourism and ecosystem services, such as watershed regulation, in addition to wood products that keep commercial forest industries globally competitive. These are all important for employment that keeps local communities viable. It is not evident which of these uses is most important, and trade-offs are obviously necessary, as the new Bighorn Country proposal demonstrates.³ The challenge is to find the right balance without repeating past mistakes.
Beetle management
A tree in the Lake Edith area of Jasper killed by the mountain pine beetle. Photo: Z. MacDonald.
Mountain pine beetle management is complicated by population threshold effects. In the endemic phase, bark-boring larvae survive in weakened trees that are widely scattered through a forest. But with drought stresses and the even-aged, mature stands of trees that fire control encourages, populations switch to an epidemic phase where, like a fire reaching a critical temperature, beetles can overwhelm trees that would normally never have succumbed. So, the strategy for controlling beetles is to get them early, monitoring carefully to see if trapping with pheromones and removing single trees is called for, or whether proactive harvesting is needed, essentially fighting fire with fire. But such strategies may not be effective on the long term, since cold winters could be the only factor sustainably holding down beetle numbers, even if intensive logging retards outbreaks on the short term.⁴ So is such logging worth the potential environmental cost?
British Columbia has learned much about mountain pine beetles, including that salvage logging of beetle-damaged forests may create new habitat conditions that preclude a return to the original state.⁵ Further, some evidence indicates that extensive salvage logging could disturb watersheds and exacerbate flooding by allowing more snow accumulation with increased snow melt in spring, and altered stream flow later in summer.⁶⁷ So, this is not only a problem for upland communities, but also cities such as Edmonton and Calgary that rely on rivers from the eastern slopes for their water supply. Such ecosystem services could outweigh the benefits of wood production.
“Some evidence indicates that extensive salvage logging could disturb watersheds and exacerbate flooding by allowing more snow accumulation with increased snow melt in spring, and altered stream flow later in summer.”
Another question is whether mountain pine beetles are adapted uniformly to conditions throughout their range and will respond the same way everywhere. Genetic studies show that southern populations in BC and Alberta are different from northern populations, with intermediates occurring in Jasper National Park.⁸ This can be used to infer the source populations of new expansions, but it remains to be seen whether mixed beetles in Jasper and Hinton are more or less viable than those to the north or south. The genetic diversity of these beetles means that there is potential for adaptability under new conditions, with added complexity contributed by different species of blue stain fungi that work with the beetles to overcome a tree. There is no guarantee that mountain pine beetles in a new area will behave the same way they did elsewhere.
It might also be helpful to reconsider even the most self-evident assumptions. One common belief is that beetle-killed trees present conditions that are significantly more prone to fire; for example, the first goal of a Town of Hinton advisory committee on mountain pine beetle was to protect the community from wildfire.⁹ A survey across the western US, however, suggests that fire risk may not actually be elevated by beetle damage.¹⁰ So a primary concern with fire may be misplaced and removing beetle-killed trees might be mainly cosmetic.
These studies show that we are still learning a lot about mountain pine beetles, their role in the environment, and what our best interests are. The potential for more beetle outbreaks on the eastern slopes of the Rockies therefore gives us a new opportunity to reconsider – and improve - how we respond to them.
Felix Sperling is a Professor in the Department of Biological Sciences at the University of Alberta.
References
1. Natural Resources Canada. Mountain pine beetle. Accessed Jan.17, 2019. https://www.nrcan.gc.ca/forests/fire-insects-disturbances/top-insects/13397 https://www.nrcan.gc.ca/forests/ fire-insects-disturbances/top-insects/13381 https://www.nrcan. gc.ca/forests/fire-insects-disturbances/top-insects/13399
2. Michelin, L. Mountain pine beetle invades Rocky area. Red Deer Advocate. Dec. 19, 2018. www.reddeeradvocate.com/news/ mountain-pine-beetle-invades-rocky-area/
3. Gerein, K. Beautiful Bighorn deserves better than ugly political games. Edmonton Journal, Jan. 10, 2019, page A2. https:// edmontonjournal.com/news/politics/keith-gerein-beautiful-bighorn-deserves-better-than-ugly-political-games
4. Natural Resources Canada. Stand development following mountain pine beetle outbreaks in south-central British Columbia. Accessed Jan. 17, 2019. http://cfs.nrcan.gc.ca/ projects/63
5. Dykstra, P.R. Are we crossing ecological thresholds by salvage logging in landscapes disturbed by mountain pine beetle? MSc thesis, Simon Fraser University. (2009) http://summit.sfu.ca/ item/9431
6. Pike, R.G., Redding, T.E., Moore, R.D., Winker, R.D., Bladon, K.D. (editors). Compendium of forest hydrology and geomorphology in British Columbia. B.C. Min. For. Range, For. Sci. Prog., Victoria, B.C. and FORREX Forum for Research and Extension in Natural Resources, Kamloops, B.C. Land Management Handbook 66. (2010). www.for.gov.bc.ca/hfd/pubs/Docs/Lmh/ Lmh66.htm ;
7. Green, K.C., Alila, Y. A paradigm shift in understanding and quantifying the effects of forest harvesting on floods in snow environments. Water Resources Research 48: W10503 (2012) https://doi.org/10.1029/2012WR012449
8. Trevoy, S.A.L., Janes, J.K., Sperling, F.A.H. Where did mountain pine beetle populations in Jasper Park come from? Tracking beetles with genetics. The Forestry Chronicle 94, 20-24 (2018). doi.org/10.5558/tfc2018-004
9. Hinton mountain pine beetle advisory committee workplan. Town of Hinton. Accessed Jan. 17, 2019 (2018) www.hinton.ca/ DocumentCenter/View/6967/HMPB-Workplan
10. Hart, S.J., Schoennagel, T., Veblen, T.T., Chapman, T.B. Area burned in the western United States is unaffected by recent mountain pine beetle outbreaks. Proc. National Academy of Sciences, USA 112, 4375-4380 (2015). https://doi.org/10.1073/ pnas.1424037112